A wide variety of materials are stored and or transported in lidded containers, where the lid is secured to the container with a clamping ring. A number of different container, lid, and clamping ring configurations have been employed.
Originally lids were secured on containers with clamping rings made of metal construction, having a generally U-shaped cross-section. However, these metal clamping rings are prone to corrode, or when painted the paint is prone to flake off, leaving particles of contamination within the container contents.
Thereafter, clamping rings of a thermoplastic construction were designed for the clamping of lids on containers without the concern for particulate contamination to the container contents. U.S. Pat. No. 4,678,216 to Gregory (1987) discloses a three piece thermoplastic clamping ring having a U-shaped cross-section, a clamping link, and a pivotable clamping lever; however, these clamping rings were not cost competitive with metal clamping rings meeting similar container performance criteria. U.S. Pat. No. 5,129,537 to Bordner (1992) discloses a two piece polymer clamping ring designed for use in securing a lid to a fiber container; however, when this design was employed to secure plastic lids on plastic containers, excessive stress was imposed upon the pivot shaft or pin integrally formed upon the pivot arm of the clamping system which caused the system to fail. U.S. Pat. No. 5,713,482 to Bordner (1998) discloses a lower profile two piece polymer clamping ring designed to provide a more secure union between the container and the lid than the previous Bordner design when used on fiber or plastic containers; however, this clamping system having a similar design in the pivot shaft or pin integrally formed upon the pivot arm of the clamping system is prone to fail in a similar fashion as the previous design.
Conventional designs include transverse molded pivot shafts on both the clamping ring and the pivot arm or lever. During the injection molding process these transverse molded pivot shafts are typically the last point where the polymer fills the mold. Because of the symmetrical nature of the clamping ring and lever, the polymer will fill the pivot shaft from both sides leaving a knit-line in the center of the pivot shaft. This knit-line is typically weaker than the surrounding polymer and may fracture under stresses induced as the lever is closed drawing the two ends of the clamping ring tight around the container and lid assembly, or fail as a result of stresses induced when the container is tipped or dropped.
Another common feature of these designs includes a receiving notch integrally molded to the clamping ring that receives the transverse molded pivot shaft. The receiving notch is generally C shaped and is prone to opening up under stress thereby allowing the pivot arm to disengage and the system will fail to clamp the lid to the container with sufficient force. U.S. Pat. No. 5,713,482 to Bordner (1998) discloses a stress transfer relationship between the two ends of the ring designed to relieve excess stress from the pivot arm and receiving notch interface; however, these features do not sufficiently engage each other to provide the required stress transfer to eliminate the breakage of the pivot arm or bending of the receiving notch in similar stress environments to those described above.
In one form of the conventional two piece polymer clamping ring assemblies, the pivot arm or lever has a cover portion extending over the receiving portion of the ring pivot shaft that is thermally or ultrasonically welded shut after assembly of the lever to the clamping ring. This feature is designed to secure the pivot shaft to the lever while allowing the two components to maintain a slideable relationship as the lever is opened and closed. The secondary plastic welding operation required to secure the two components together adds manufacturing cost to the assembly.
The present invention is directed at solving one or more of the problems discussed above in a novel and simple manner.